1. Field of the Invention
The present invention generally relates to a liquid-droplet jet head having plural nozzles discharging liquid droplets, a liquid discharging apparatus including the liquid-droplet jet head, and an image forming apparatus including the liquid discharging apparatus.
2. Description of the Related Art
Image forming apparatuses operate by discharging liquid droplets onto recording sheets such as paper to form images on the recording sheets. Such an image forming apparatus generally includes a liquid-droplet jet head having plural nozzles communicated with pressure liquid chambers, and pressure converters (actuators) provided to the corresponding pressure liquid chambers.
FIG. 1 is a view illustrating one example of a liquid-droplet jet head according to a related art.
A liquid-droplet jet head 10 includes a vibration board 3 partially forming a wall surface (hereinafter also called as “first surface of the vibration board”) of a pressurized chamber 2 communicated with a nozzle 1, and an actuator 5 provided on a supporting substrate 4. In the liquid-droplet jet head 10, the vibration board 3 and the actuator 5 are connected via a connecting unit 6. The vibration board 3 is elastically deformed with displacement of the actuator 5. A second surface of the vibration board 3 (i.e., the other side of the wall surface of the pressurized chamber 2) is less rigid than other surfaces forming the pressure liquid chamber 2 to efficiently change the capacity of the pressure liquid chamber 2 by displacing the actuator 5.
The pressure liquid chamber 2 is connected to a common liquid chamber 9 via a fluid resistor 7 and a communicating unit 8. The common liquid chamber 9 is also connected to an unshown ink tank. The actuator 5 is deformed based on the voltage applied by an unshown driving circuit, and the vibration board 3 is deformed based on the deformation of the actuator 5 so as to increase or decrease the capacity of the pressure liquid chamber 2. Increasing the capacity of the pressure liquid chamber 2 results in a decrease in internal pressure of the pressure liquid chamber 2, thereby supplying ink to the pressure liquid chamber 2 from the common liquid chamber 9 via the communicating unit 8 and the fluid resistor 7. In contrast, decreasing the capacity of the pressure liquid chamber 2 by driving the actuator 5 results in an increase in the internal pressure of the pressurized chamber 2, thereby discharging the ink from the nozzle 1. The discharged ink forms scattered liquid droplets (i.e., ink droplets), and the scattered liquid droplets are adhered to an unshown recording medium (e.g., paper), thereby forming an image on the recording medium.
FIG. 2 is a cross sectional view of the liquid-droplet jet head 10 taken along the line A-A of FIG. 1. The actuator 5 includes driving actuators 5a arranged at positions to face the corresponding pressure liquid chambers 2, and supporting actuators 5b arranged at positions to face corresponding partitions 11 which partitions adjacently arranged pressure liquid chambers 2. The aforementioned structure of the liquid-droplet jet head 10 is hereinafter called a “bi-pitch structure”. In the liquid-droplet jet head 10 having this bi-pitch structure, voltage is applied to the driving actuators 5a to deform the vibration board 3, whereas no voltage is applied to the supporting actuators 5b. The supporting actuators 5b are utilized for fixating the pressure liquid chambers 12 to the supporting substrate 4.
It is preferable that the nozzles 1 be arranged as densely as possible in the liquid-droplet jet head 10 so as to carry out processing with increased speed and provide higher quality of images. However, since the liquid droplet jet head 10 having the bi-pitch structure includes both the driving actuators 5a and the supporting actuators 5b, the number of the actuators 5 to be arranged is twice as many as the number of the nozzles 1 in total. Accordingly, it is generally difficult to manufacture such a liquid droplet jet head 10.
Then, it is suggested that the liquid droplet jet head 10 include the actuator 5 consisting only of the driving actuator 5a as shown in FIG. 3. Such a structure is hereinafter called a “normal-pitch structure”. FIG. 3 is a view illustrating another example of the liquid-droplet jet head 10 according to the related art.
The liquid droplet jet head 10 having the normal-pitch structure only includes half the number of actuators 5 as compared to that of the liquid-droplet jet head 10 having the bi-pitch structure, and hence is suitable for manufacturing an increased number of nozzles.
However, since the liquid droplet jet head 10 having the normal-pitch structure includes no supporting actuators 5b, the pressure liquid chambers 12 are not sufficiently supported. Thus, the pressure liquid chambers 12 and nozzle plates 13 are pushed up by thrust force of the driving actuators 5a, thereby generating a crosstalk. The more the number of bits generated by driving the driving actuators 5a there is, the more thrust force may be generated by the driving actuators 5a, thereby increasing an adverse effect of the crosstalk on the characteristics of the jets. Thus, the characteristics of the jets vary with the increase or decrease in the number of bits generated by driving the actuators 5a. 
In order to suppress such a crosstalk in the liquid droplet jet head 10 having the normal-pitch structure, Japanese Patent No. 3381678 and Japanese Patent No. 3248486 disclose technologies in which an inactive region of a piezoelectric element is polarized such that both ends of the inactive region are utilized as supporting pillars, thereby leaving the both ends of the inactive region electrically floating.
However, in the disclosed technologies of both Japanese Patent No. 3381678 and Japanese Patent No. 3248486, since the piezoelectric element needs to have a deep groove in order to form the supporting pillars, the supporting pillars may each have a shape with an extremely high aspect ratio. Accordingly, the supporting pillars of the piezoelectric element may develop fractures during the manufacturing process. Further, with such technologies, since some of the internal electrodes are cut off, arrangement of the electrodes in the inactive regions of the piezoelectric element may become complicated.